Sam Witham – Conservation Research Student
This summer I collected 10,000 (approx.) native raspberry seeds Rubus idaeus from the North York Moors for the UKNTSP (UK National Tree Seed Project). This is a project run by Kew to collect tree and shrub seeds from different regions of the UK in order to build a genetic representation of all UK tree/shrub species in the country. I first got involved with the project when I first started with the National Park last autumn.
A couple of weeks ago I got to visit the Kew Millennium Seed Bank at Wakehurst Place in West Sussex to drop off the raspberry seeds and see behind the scenes. Bede West, a field officer for the UKNTSP, kindly gave me a tour of the Seed Bank, and explained the processes involved.
Collected seeds are sent, along with a herbarium (plant) specimen, to the Millennium Seed Bank. The herbarium specimen is used to determine the correct plant species and is then stored at the Herbarium at Kew Gardens.
If seeds are not yet ripe, they are ripened in a ripening room.
Once the paper work has been checked over, the seeds are extracted from casing or fruit, and washed using inventive methods such as squashing them while wearing wellies, scrubbing them on a rubber car matt, sieving them, and rinsing them in the sink. A zigzag aspirator can be used to separate seeds by size.
Most seeds are then x-rayed. Seeds can be infected by pathogens such as grubs, fungi, viruses and bacteria, reducing their viability. Viruses can be hard to detect in the x-ray so a sample of seeds can also be looked at under a microscope.
There are orthodox, recalcitrant or unorthodox seeds, along with intermediate seeds. Orthodox seeds can be dried to 5% moisture content or lower and then frozen. Relcalcitrant seeds will not survive if their moisture content drops below 40%. Intermediate seeds are someway inbetween and can be dried somewhat.
Orthodox seeds are placed in a temperature and humidity controlled drying room where the seeds are gradually dried to 5% moisture or lower. Certain seeds can take more than six months to dry out. The seeds needs to be dried so that damaging water crystals do not form when they are frozen.
At some point before the seeds go into storage, 50 seeds from a collection are weighed and then the whole seed collection is weighed. From this the mean seed weight is calculated.
There are two types of vault rooms – active rooms and base rooms. The seeds in the base rooms are left undisturbed, while seeds from the active rooms are used for research and regular monitoring. After seeds have been frozen, an initial seed sample is warmed up and germinated to test for viability. Samples are then taken from the underground freezer every ten years and germinated in order to monitor their continuing viability. This is done until there are no longer enough active room seeds to do this. The remaining frozen seeds are then moved to a base room and are also left undisturbed. At this point it’s time to collect more seeds from the wild.
Seeds are germinated on agar, a jelly-like substance taken from algae. Certain nutrients can be added to the agar to meet the requirements of the seeds. The seeds are kept at temperatures and humidities matching their country of origin, and some seeds are moved from light rooms to dark rooms to simulate day and night. Some seeds can be more demandng and extra steps need to be taken to improve germination such as subjecting them to different climatic conditions and adding chemicals.
Once the active room seeds have been germinated and counted they are often destroyed, although Kew is looking into being able to grow more of them on in a nursery. Some seeds are grown on in greenhouses to definitively ascertain species and to create herbarium specimens, and also if they have been requested by outside organisations.
The recalcitrant seeds that could not survive the drying and freezing processes include coconuts, brazil nuts and acorns. Currently these seeds are germinated and the embryos are then cryogenically frozen in liquid nitrogen at -196oC. This method is being actively researched and developed because as yet its not been that successful.
The value of the seeds stored at the Millennium Seed Bank is as a research resource, and as a living natural heritage archive which can be used to boost wild plant populations if plants become rare.
Thanks to the Millennium Seed Bank, and thanks to the Society for National Park Staff for paying my expenses.